The present invention relates to processes for making partially-oriented polyamide yarns for textile applications.
Partially-oriented polyamide yarns are in widespread use as feed yarns for draw texturing and other uses. Various processes are known for manufacturing such feed yarns. In one such process, polyamide polymer is melt-spun at a withdrawal speed sufficient to produce a yarn as spun having an elongation less than 175%. In a coupled drawing step, the yarn is then drawn sufficiently to produce the partially-oriented nylon yarn with an elongation in the range of 50-100 percent. For some enduses, however, this coupled spin-draw process sometimes does not provide partially-oriented nylon yarns with a desired degree of dye uniformity.
When it is attempted to use a heated fluid jet such as that disclosed in Geerdes et al, U.S. Pat. No. 3,452,131, to localize the draw point in this process, dye uniformity is improved. However, the heated fluid jet causes loops of the filaments of the yarn to form and to extend outwardly from the yarn bundle. The filament loops decrease the quality of the yarn and make the process commercially unacceptable at spinning speeds above 2200 yards per minute (2000 meters per minute). For example, using steam at 20 pounds per square inch (138 kPa) and 135.degree. C. with a 1.5.times. draw ratio, filament loops as high as 80 loops/million-end-yards (yards of yarn multiplied by number of threadlines tested) (88 loops/million-end-meters) were observed. The problem increases with higher steam pressures and/or when higher relative viscosity polymer is used.